1. Field of the Invention
The present invention relates to a non-aqueous electrolytic cell including a positive electrode, a negative electrode, and a non-aqueous electrolyte.
2. Description of the Relates Arts
Conventionally, a nickel-cadmium cell, a lead cell, and the like have been used as secondary cells for electronic apparatuses. However, with the recent progress in the electronic technology, many of he electronic apparatuses have become smaller and portable, which requires increase of high energy density of the secondary cell for the electronic apparatuses. However, the nickel-cadmium cell or the lead cell has a low discharge voltage and cannot increase the energy density sufficiently.
To cope with this, a so-called lithium-ion cell is studied and developed. The lithium-ion cell has advantages that the discharge voltage is high and the cycle service life is long because of little self discharge. The lithium-ion cell is a non-aqueous electrolytic secondary cell in which the negative electrode is made from a carbon material capable of doping and dedoping lithium ions and the positive electrode is made from a lithium transition metal composite oxide.
In such a lithium-ion cell, firstly, during a charge process, lithium ions are discharged from the positive electrode, after which the lithium ions are inserted between carbons of the negative electrode to form a compound with the carbons. This phenomenon is called doping. During a discharge, lithium atoms contained in the compound of the negative electrode become lithium ions, which are discharged from the negative electrode and again becomes the aforementioned LiMxOY in the positive electrode. This phenomenon is called dedoping. That is, in a lithium-ion cell, electric energy is generated by movement of lithium ions.
In order to improve cell characteristics such as the cell initial capacity, internal resistance, and the like in the aforementioned non-aqueous electrolytic cell, the characteristic of the negative electrode is very important in addition to the characteristics of the positive electrode and the non-aqueous electrolyte.
The negative electrode is made from a substance capable of doping and dedoping lithium ions. There can be exemplified a carbon material, a crystalline metal oxide, non-crystalline metal oxide, and the like. The carbon material may be, pyrocarbon, coke, graphite, vitreous carbons, active carbon, or the like.
However, the non-aqueous electrolytic cell produced using the aforementioned material has a problem that when used at a low temperature, lithium ion doping and dedoping cannot be performed smoothly in the negative electrode and it is impossible to obtain a sufficient cell characteristic.
It is therefore an object of the present invention to provide a non-aqueous electrolytic cell having a preferable cell characteristic at a low temperature. In order to achieve the aforementioned object, the non-aqueous electrolytic cell according to the present invention includes a negative electrode capable doping and dedoping lithium ions, a positive electrode capable of doping and dedoping lithium ions, and a non-aqueous electrolyte, wherein the negative electrode contains fiber carbon.
The non-aqueous electrolytic cell according to the present invention having the aforementioned configuration exhibits preferable cell characteristics at a low temperature.